It however does not have issues maintaining the temperature when it’s not actually printing. I can set my hotend to 215 before beggining my print and it’s happy to sit there.
Other problems with it include under extrusion and extruder skipping, as it seems to have troubles pushing the filament out.
What does this sound like it could be? Does it sound like a blockage? Could a blockage cause temperature issues? I have already tried turning off the part cooling fan as I had a similar issue with that a while back but that has no made a difference it seems.
Hmm I hadn’t considered that the reading could be wrong, I’ll pull apart my hotend later today to have a look at it.
It’s a pretty new printer though, I’d be surprised if I have managed to wear down the wire yet, but still I’ll have a look.
Does your Ender 3 still have the screwed-on-cable type of thermistor? These ones break when overtightened, which can happen at the factory.
If the cable and thermistor is turns out to be fine, run a PID tuning.
Check the entire thermistor cable as well as the plug connections for tightness. Preheat the hotend and then wiggle/bend the cable 1 inch at a time all the way back to the main board plug checking to ensure the recorded temp remains constant. (You can also do this with an accurate multimeter checking resistance across the unplugged thermistor if you don’t want the printer on while poking around.)
Those aggressive jumps sure look like a thermistor problem, but only when printing in motion, which screams bad cable/connection. Manufacturing errors happen.
Luck of the draw, could be bad out of the gate, my prusa mk3 had the exact same thing happen less than a month after running it. If you can, add a pinned connection, makes swapping thermistors super easy as a lot of places sell cartridges with microfit connectors.
When I had it happen it wasn’t always a problem, was only on certain movements and then it’d error on thermal runaway. I’d say change it anyhow as it’s simple to do and you eliminate a cause, best to start with the easy things.
I had a similar problem caused by loose thermistor wiring, similar to what other people here are suggesting. I used an extra zip tie to secure the wire so it doesn’t wiggle during printing, and the issue was fixed for me.